1. Field of the Invention
The present invention relates generally to an ATM cell buffer read control system and a control method. More particularly, the invention relates to an ATM cell buffer read control system and a control method which can effectively use a band by distributing an extra band according to number of output ATM cells per connection with guarantee of minimum output band per connection in accordance with ratios of output ATM cell number per a preliminarily set given period.
2. Description of the Related Art
Conventionally, there has been proposed a read control system employing Weight Round Robin (WRR) as one read system in an ATM cell buffer control portion.
In the WRR system, selecting operation for outputting data with different weights is performed for guarantee of minimum speed of data output according to ratio of the weight for respective queues and extra output line capacity is distributed according to weight for respective queues.
Examples of ATM cell buffer reading control system has been disclosed in Japanese Unexamined Patent Publication No. Heisei 7-66807 (hereinafter referred to as prior art 1), Japanese Unexamined Patent Publication No. Heisei 8-340336 (hereinafter referred to as prior art 2), Japanese Unexamined Patent Publication No. Heisei 9-162906 (hereinafter referred to as prior art 3) and Japanese Unexamined Patent Publication No. Heisei 9-238147 (hereinafter referred to as prior art 4).
The prior art 1 disposes cell out of a range of band. The prior art 2 causes fluctuation to a range of band depending upon necessity. The prior art 3 outputs ATM cells in sequential descending order of weights, and inhibits outputting of cell when number of cells exceeds a threshold value. The prior art 4 performs modification of band utilizing a vacant band.
However, in the read control system employing the WRR system, if extra capacity is excessively large, an output rate from a particular queue is increased to cause input rate error in a User Parameter Control (UPC) function portion in an ATM line receiving terminal in the next stage to cause disposal of the ATM cells.
Means for solving the problem in such system has not been disclosed in any of the foregoing prior arts 1 to 4.
Therefore, it is an object of the present invention to provide an ATM cell buffer read control system and a control method which can prevent occurrence of over-rate due to excessive use of extra line capacity with guarantee of minimum output rate in a WRR system.
In order to accomplish the above-mentioned object, according to the first aspect of the present invention, an ATM cell buffer read control system for effectively using a band by distributing an extra band with a ratio of number of ATM cell number per connection with guarantee of minimum output band per connection according to preliminarily set ratio of output ATM cell number per a given period, comprises:
judgment means for making judgment whether the output band after distribution of said extra band falls within a reference output range.
According to the second aspect of the present invention, an ATM cell buffer read control method for effectively using a band by distributing an extra band with a ratio of number of ATM cell number per connection with guarantee of minimum output band per connection according to preliminarily set ratio of output ATM cell number per a given period, comprises:
a first process of making judgment whether the output band after distribution of said extra band falls within a reference output range.
According to the foregoing first and second aspects of the present invention, the judgment means and the first process make judgment that the output bands after distribution of the extra band fall with the reference output band.
On the basis of the result of judgment, it is determined whether the ATM cell is to be output or not. Therefore, it is at least possible to avoid problem to output the ATM cell without checking to cause over-rate due to excessive use of extra line capacity and thus result in violation of UPC in the UPC function portion in the ATM line receiving terminal in the next stage to result in disposal of the ATM cell.